Rectus sheath block results in greater cranial-caudal spread whereas transversus abdominis plane block results in greater lateral spread as assessed by computed tomography in dogs.

Abstract

To evaluate the in vivo spread of iodinated contrast following injections in the transversus abdominis plane (TAP) and rectus sheath in anesthetized dogs via computed tomography. Secondarily, the time of performing each block was compared. 6 adult, purpose-bred Beagles. In a prospective crossover study, dogs were administered injections either in the rectus sheath or transversus abdominis fascial plane in the same manner as a rectus sheath block (RSB) or TAP block using dilute iodinated contrast. Computed tomography scans were performed immediately following injection (time [T]-0) and at 3, 9, 18, and 30 minutes postinjection. Data regarding the spread in the cranial-caudal and lateral directions and time to perform the injections were compared between the 2 techniques using paired or 2-sample t tests. There was significantly greater spread in the cranial-caudal direction in the RSB group (62.9 ± 6.4 mm vs 54.8 ± 6.8 mm at T30; P = .009), whereas spread in the lateral direction was greater in the TAP group (37.3 ± 3.0 mm vs 48.6 ± 6.1 mm at T30; P < .0001). The RSB injection was performed in a more time-efficient manner than TAP injection (48.2 ± 3.2 seconds vs 82.3 ± 8.7 seconds; P = .03). In living subjects, RSB injections resulted in greater cranial-caudal spread while TAP injections resulted in greater lateral spread. Rectus sheath block injections were performed in a more time efficient manner compared to a single point TAP injection in anesthetized dogs. The RSB was performed in a more time-efficient manner and would likely result in greater coverage of the ventral midline. The TAP block would likely result in more significant regional anesthetic coverage of the lateral abdominal wall. Further studies are required to determine the degree of the clinical significance of these results.